Hollow fan blade for turbine engine and method of manufacturing such a blade

ABSTRACT

The invention relates to a method of manufacturing a single-piece hollow fan blade for turbine engines comprising a foot ( 2 ) extended by a rotor blade ( 4 ) in a radial direction, the method comprising the following stages: 
         making via forging of a single-piece fan blade ( 1 ) with a plurality of inserts; and    eliminating of the inserts so as to obtain a plurality of recesses ( 16 ) in this blade.        

     The invention also relates to such a blade ( 1 ) fitted with a plurality of recesses ( 16 ) each extending substantially and radially along a curved central line ( 18 ).

TECHNICAL FIELD

The invention relates to the field of hollow blades for turbine engine, and more particularly to those of hollow fan blades with large chord.

Furthermore, the invention also relates to the method of manufacturing such blades.

STATE OF THE PRIOR ART

In the prior art, fan blades with large chords for turbine engines notably made their appearance in the embodiment of rotor fan blades for double flow turbine engines.

Indeed, this type of blade has proved to be entirely appropriate to satisfy the severe operating conditions, and further integrates satisfactory mechanical characteristics as well as good anti-vibration properties and shock resistant qualities from foreign objects.

In order to obtain high speed at the end of the blade, a mass reduction operation was rapidly proposed, by notably presenting hollow blades.

In this regard, the making of hollow fan blades for turbine engines firstly consisted in using techniques of hot-press moulding of shell elements or diffusion bonding of two half blades type, this diffusion bonding technique having been notably associated with that of superplastic forming.

However, even though these known techniques made it possible to make hollow fan blades with large chords, the implementing of these remain relatively complex and expensive.

To overcome this inconvenience, the designing of a single-piece hollow fan blade was proposed, in which recesses were envisaged so as to reduce the overall mass.

Usually, the method of manufacturing of such a blade consists in making a singe-piece blade via forging, then machining a plurality of holes so as to obtain the desired recesses.

The document U.S. Pat. No. 5,407,326 discloses such a method, in which the recesses are substantially made transversally according to the thickness of the rotor blade. Once these recesses have been made, it is necessary to blank them off using plugs, in order to ensure the continuity of the upper and lower surfaces of the blade.

To accomplish this, plugs are generally welded to the blade through high energy beam, which renders the method of manufacturing timely and expensive, these inconveniences being particularly accentuated due to the large number of transversal recesses envisaged to ensure a significant reduction in the overall mass of the blade.

Thus, the making of recesses extending substantially radially was proposed, as the document EP-A-0 924 381 notably discloses. This type of recess is advantageous in that it usually emerges around the foot of the blade, and that it does not modify the upper and lower surfaces of this blade. Consequently, it is no longer essential to carry out the fitting of a multitude of plugs onto the established recesses, so that the method of manufacturing is better optimised than that which incorporates the implementing of transversal recesses.

Nevertheless, the standard machining operations to make the radial holes do not allow to obtain recesses of any great length, to the extent that the machined holes extend along a straight line non-adapted to the curved shape of the blade. By way of illustration and still in reference to the document EP-A-0 924 381, the radial recesses principally extend around the foot of the blade, but hardly prolong into the curved part of the rotor blade in order to avoid emerging beyond it, and thus again require the attaching of plugs ensuring the continuity of the upper and lower surfaces.

Thus, the radial recesses encountered can only have short lengths due to the major twisting encountered on such fan blades, and consequently only participate in a largely insignificant manner to the reduction of the overall mass of the single-piece blade.

OBJECT OF THE INVENTION

The purpose of the invention is therefore to propose, on one hand a method of manufacturing a single-piece hollow fan blade for turbine engines, and on the other hand such a single-piece hollow fan blade for turbine engines the blade and the method of manufacturing resolving at least partially the aforementioned inconveniences regarding the embodiments of the prior art.

To accomplish this, the first object therefore of the invention is a method of manufacturing a single-piece hollow fan blade for turbine engines comprising a foot extended by a rotor blade in a radial direction, the method comprising the following stages:

-   -   making via forging of a single-piece fan blade with a plurality         of inserts; and     -   eliminating of the inserts so as to obtain a plurality of         recesses in this blade.

Advantageously, the recesses are not obtained via machining operations, but through a simple elimination stage of the inserts attached to the blade, these inserts having been preferably deformed during the production stage via forging of the single-piece blade.

In this manner, these recesses no longer necessarily extend along a straight line as those obtained via standard machining, but can on the contrary extend along a curved line.

This specificity is particularly advantageous in the framework of the making of radial recesses, to the extent that the latter can thus extend along a large radial length without emerging around the upper and lower surfaces, by substantially following the profile of the blade.

Thus, the length of the radial recesses is no longer influenced by the curved form of the fan blade, and the reduction in mass resulting from the presence of these recesses can thus be significant.

Of course, this rapid and low cost method of manufacturing can also be implemented for the making of recesses extending along every direction through the blade, without diminishing the framework of the invention.

Preferably, as indicated above, the production stage via forging of the single-piece blade fitted with a plurality of inserts is carried out so that the obtained recesses, following the elimination stage of said inserts, each extend substantially and radially along a central curved line.

In this regard, it is indicated that a digital simulation of the forging operations makes it possible to easily envisage the final positions of the recesses in the blade, as well as their final form.

In a first preferred embodiment of the method of manufacturing according to the invention, the production stage via forging of the single-piece fan blade fitted with a plurality of inserts is carried out from a supply element with a plurality of inserts.

In such a configuration, the method is particularly simple and rapid to implement.

In a second preferred embodiment of the method of manufacturing according to the invention, the production stage via forging of the single-piece fan blade fitted with a plurality of inserts is carried out via the implementing of the following operations:

-   -   prior forging of a standard supply element;     -   installing of the plurality of inserts in the previously forged         standard supply element;     -   forging of the previously forged standard supply element and         fitted with the plurality of inserts, so as to obtain the         single-piece fan blade fitted with a plurality of inserts.

In the two preferred embodiments of the method described above, it can be envisaged that the elimination stage of the inserts is carried out via solvolysis, these inserts preferably being made in a material taken from the group composed of steels, minerals and composites. In this regard, it is naturally indicated that the solvolysis must be performed so that the agent(s) used ensure the dissolution of the component material of the inserts, without attacking the blade generally made in titanium or one of its alloys.

As always in a preferable manner, the initial form of the inserts is indifferently cylindrical or non-cylindrical, and of circular or non-circular section.

Finally, in a continual manner, the method of manufacturing is carried out so that the elimination stage of the inserts is followed by a finishing stage of the blade.

Furthermore, the object of the invention is also a single-piece hollow fan blade for a turbine engine comprising a foot extended by a rotor in a radial direction, this blade being fitted with a plurality of recesses each extending substantially and radially along a central line, each central line being a curved line.

As previously mentioned, the radial extension along curved lines advantageously allows the recesses to have a considerable length, to the extent that they can radially extend by following the curved profile of the blade, without emerging onto the upper and lower surfaces.

The reduction in mass resulting from the presence of these radial recesses can thus be significant, particularly when the blade is designed so that at least one recess is made so as to radially and entirely pass through this fan blade.

Naturally, it is also possible that at least one recess is made so as to radially pass through this blade only partially, without dismissing the framework of the invention.

Finally, at least one recess of the blade is preferably of non-constant section along the curved line.

Other advantages and characteristics of the invention will appear in the non-restrictive detailed description below.

BRIEF DESCRIPTION OF THE DRAWINGS

This description will be made in relation to the annexed drawings among which;

FIG. 1 represents a perspective view of a first preferred embodiment of the single-piece hollow fan blade according to the invention;

FIGS. 2 a to 2 c diagrammatically illustrate different stages of a first preferred embodiment of the method of manufacturing according to the invention;

FIGS. 3 a to 3 e diagrammatically illustrate different stages of a second preferred embodiment of the method of manufacturing according to the invention;

FIG. 4 represents a perspective view of a second preferred embodiment of the single-piece hollow fan blade according to the invention;

FIG. 5 represents a perspective view of a third preferred embodiment of the single-piece hollow fan blade according to the invention; and

FIGS. 6 to 8 represent different forms that the inserts can take following the production stage via forging of the single-piece fan blade fitted with the plurality of inserts, during the implementing of the method of manufacturing according to the invention.

DETAILED PRESENTATION OF THE PREFERRED EMBODIMENTS

In reference to FIG. 1, we can notice a single-piece hollow fan blade 1 for turbine engines (not represented), according to a first preferred embodiment of the invention.

This single-piece hollow fan blade 1, of fan rotor blade type with large chord, comprises a foot 2 extended by a rotor blade 4 in a radial direction.

The rotor blade 4, intended to be placed in the circulation path of an airflow of the turbine engine, has two external surfaces 6 and 8, respectively called upper surface 6 and lower surface 8, connected by a leading edge 10 and a trailing edge 12. Furthermore, it has been noticed that the latter can have an intermediary part 14 between the foot 2 and the rotor 4, this part 14 also being called “connection pole”.

As can be seen in FIG. 1, the single-piece hollow fan blade 1, for example made in a titanium alloy, is fitted with a plurality of recesses 16 each extending substantially radially according to a central line 18 (only the three recesses 16 closest to the leading edge 10 are represented entirely). In order to ensure a considerable length for each of these recesses and without them emerging around the upper and lower surfaces 6 and 8, each of the central lines 18 is a curved line, capable of radially following the profile of the blade.

In a first preferred embodiment, each recess 16 extends into the blade 1 so as to pass entirely and radially through it, that being by emerging on one hand around a lower end 20 of the foot 2, and on the other hand around an upper end 22 of the rotor blade 4.

Furthermore, it can be envisaged that at least one recess 16 has a non-constant section along its central line 18, as represented in FIG. 1. Indeed, in this preferred embodiment, the section of the recesses 16 is greater around the foot 2 than around the rotor blade 4. This capacity to vary the section of the recesses 16 thus advantageously allows to adapt the volume of withdrawn material to the local thickness of the blade, still so as to obtain a maximum reduction in the overall mass of this blade 1, whilst allowing it to maintain satisfactory mechanical properties. Likewise, it is possible to envisage recesses of considerably section around the centre of the blade 1, and recesses whose sections progressively diminish in size as they get closer to the leading edge 10 and the trailing edge 12.

In reference to FIGS. 4 and 5, we can see a single-piece hollow fan blade 1 for turbine engines, respectively according to a second preferred embodiment of the invention.

In these two preferred embodiments, recesses as always extend radially in the single-piece hollow fan blade 1 along curved central lines, but in a manner so as to only partially pass through this said blade 1.

As can be seen in FIG. 4, blind recesses 116 extend along curved central lines 118 so as to emerge at the upper end 22 of the rotor blade 4, just as the recesses 16 of the first preferred embodiment described above. However, these recesses 116 do not extend as far as the foot 2, but only to a central section of the blade 1, substantially placed half way up in the radial direction of the latter.

Furthermore, as can be seen in FIG. 5, blind recesses 216 extend along curved central lines 218 so as to emerge at the lower end 20 of the foot 2, just as the recesses 16 of the first preferred embodiment described above. However, these recesses 216 do not extend as far as the upper end 22 of the rotor blade 4, but only to a central section of the blade 1, substantially placed half way up in the radial direction of the latter.

Of course, it is also possible to envisage a single-piece fan blade 1 incorporating differently designed recesses such as those presented in the description of the first, second and third preferred embodiments, without dismissing the framework of the invention. In this regard, it is indicated that the sought after mechanical characteristics for the blade 1 influence the number of these recesses, as well as their sections and lengths.

In reference to FIGS. 2 a to 2 c, different stages of a first preferred embodiment of the method of manufacturing according to the invention are represented diagrammatically.

FIG. 2 a illustrates a supply element 24 equipped with a plurality of inserts 26, this supply element 24 being intended to undergo a forging stage consisting in one or several successive operations, in order for it to have the form of a blade.

The inserts 26 integrated into the supply element 24, indifferent to the initial cylindrical or non-cylindrical form, are for example made using steels, composites or minerals, whereas the supply element 24 is preferably made in a titanium alloy.

After having undergone this forging stage implemented according to known techniques, the supply element 24 then has the form of a blade 1 such as is represented in FIG. 2 b, fitted with inserts 26 placed in the same locations as those intended for the recesses of this blade. In referring to this FIG. 2 b, we can see that the inserts 26, each of which was initially in the form of two stacked coaxial cylindrical sections and of circular sections (FIG. 2 a), have also been deformed during the forging stage.

Naturally, a digital simulation of the forging operations easily allows to envisage the final positions of the inserts 26 in the supply element 24 as well as the definitive shapes of these said inserts, according to an initial specific configuration of the supply element 24 fitted with inserts 26.

In this preferred embodiment, as represented in FIG. 2 c, corresponding to a transversal view of FIG. 2 b along plane P, the forging stage leads the inserts 26 to be fitted along a chard 30 of the blade 1, and to have a substantially oval section of which the two flattened ends are centred on this said chard 30.

Of course, as mentioned above, the final section of the inserts 26 can vary according to the deformation mode employed, the initial positioning of the inserts in the supply element 24, as well as according to the initial shapes of these inserts 26 and of the supply element 24.

By way of illustration, FIGS. 6 to 8 represent various forms, other than those substantially oval, that can receive the inserts 26 initially having cylindrical sections of circular sections, following the forging stage of the supply element 24.

FIG. 6 shows an insert 26 fitted with a supply element 24 having undergone a major deformation during the forging stage. The section of this insert 26 thus has the form of a band extending substantially according along the chord 30 of the blade 1, and whose central part if slightly thinner than the two end parts.

FIGS. 7 and 8 show inserts 26 equipping a supply element 24 having undergone a minor deformation during the forging stage. The sections of these inserts 26, generally of oval shape similar to the one represented in FIG. 2 c, are such that respectively one or the two flattened ends are substantially and progressively tapered along the chord 30 of the blade 1.

Once this stage has been carried out, an elimination stage of the inserts 26 is then performed, so that the latter give way to recesses of the same shape.

This stage is preferably carried out via a solvolysis of the inserts 26, for example by submerging the blade 1 fitted with these inserts 26 into a bath of appropriate agent, that does not engender a deterioration of the blade.

Thus, a single-piece hollow fan blade 1 is obtained such as the one represented in FIG. 1, whose recesses 16 thus extend along curved central lines 18 identical to the curved central lines 28 along which extend the inserts 26 through the supply element 24, before the latter are eliminated.

Finally, this stage can thus be followed by a standard finishing stage of the blade 1, intended to strictly give it the desired airfoil profile.

In reference to FIGS. 3 a to 3 e, different stages of a second preferred embodiment of the method of manufacturing according to the invention are represented diagrammatically.

In this preferred embodiment, only the first production stage via forging of a single-piece fan blade fitted with a plurality of inserts differs in comparison to the method described in the previous preferred embodiment.

Indeed, the implementing of a prior forging operation for a standard supply element 32 is first carried out, such as the one represented in FIG. 3 a.

This standard supply element 32 is preferably made in a titanium alloy, and has a substantially cylindrical form of circular section.

The prior forging operation can thus consist in one or several successive forging operations, preferably only one, whose purpose is to obtain a previously forged supply element 32, such as a preform with the approximate shape of a blade as shown in FIG. 3 b.

Then, on this previously forged supply element 32, a plurality of holes 34 intended to receive the inserts is made, as can be seen in FIG. 3 c. In this regard, it is specified that the making of these holes 34 is performed using standard techniques such as machining. Furthermore, it is obvious that the sought after mechanical characteristics for the blade 1 define the number of holes 34 to be envisaged, as well as their sections and lengths. By way of illustration, the created holes 34 are cylindrical and of constant section. Moreover, the sections of holes 34 can be very large for those located near the centre of the preform, and of diminishing size closer these holes 34 get to the edges of this preform, as clearly illustrated in FIG. 3 c. Naturally, the feasibility criterion of holes 34 in the preform also arises in the setting of the maximum dimensions that can be applied for these holes 34.

Once the holes 34 have been made in a substantially radial direction of the preform, the inserts 26 of complimentary form, thus also cylindrical and of circular section, are effectively places on the inside of the latter, as illustrated in FIGS. 3 d and 3 e.

Thus a forging operation can be carried out on the previously forged standard supply element 32 and equipped with the plurality of inserts 26, so as to obtain a single-piece blade fitted with a plurality of inserts 26. The obtained blade is thus similar to the one represented in FIG. 2 b, except that the deformed inserts 26 each have a substantially constant section along its associated curved line 28, due to the initial cylindrical form of these inserts 26.

As in the previous preferred embodiment, the final section of the inserts 26 can vary according to the deformation modes employed, the positioning of the inserts 26 in the previously forged supply element 32, as well as according to the initial shapes of these inserts 26 and of the previously forged supply element 24.

Subsequently, the elimination and finishing stages are substantially identical to those described in the first preferred embodiment of the method according to the invention.

Of course, various modifications can be introduced by those skilled in the art into the method of manufacturing the single-piece hollow blade 1 which has just been described, solely by way of non-restrictive illustration. 

1. Method of manufacturing a single-piece hollow fan blade for turbine engines comprising a foot extended by a rotor blade in a radial direction, characterised in that it comprises the following stages: making via forging of a single-piece fan blade with a plurality of inserts; and eliminating of inserts so as to obtain a plurality of recesses in said blade.
 2. Method of manufacturing set forth in claim 1, characterised in that the production stage via forging of the single-piece blade fitted with a plurality of inserts is carried out so that the obtained recesses, following the elimination stage of the inserts, each extend substantially and radially along a curved central line.
 3. Method of manufacturing set forth in claims 1 or 2, characterised in that the production stage via forging of the single-piece hollow fan blade fitted with a plurality of inserts is carried out from a supply element equipped with said plurality of inserts.
 4. Method of manufacturing set forth in claim 1 or 2, characterised in that the production stage via forging of the single-piece hollow fan blade fitted with a plurality of inserts is carried out via the implementing of the following stages: prior forging of a standard supply element installing of said plurality of inserts in the previously forged standard supply element forging of the previously forged standard supply element and fitted with said plurality of inserts, so as to obtain said single-piece fan blade fitted with a plurality of inserts.
 5. Method of manufacturing set forth in claim 1, characterised in that the elimination stage of said inserts is carried out via solvolysis of these inserts.
 6. Method of manufacturing set forth in claim 1, characterised in that each insert is made in a material taken from among the group constituted of steels, minerals and composites.
 7. Method of manufacturing set forth in claim 1, characterised in that the initial form of said inserts is indifferently cylindrical or non-cylindrical.
 8. Method of manufacturing set forth in claim 1, characterised in that the elimination stage of said inserts is followed by a finishing stage of said blade.
 9. Single-piece hollow fan blade for a turbine engine comprising a foot extended by a rotor blade in a radial direction, said blade being fitted with a plurality of recesses each extending substantially and radially along a central line, characterised in that each central line is a curved line.
 10. Blade set forth in claim 9, characterised in that at least one recess is made so as to radially and entirely pass through said blade.
 11. Blade set forth in claim 9, characterised in that at least one recess is made so as to radially pass through said blade only partially.
 12. Blade set forth in claim 9, characterised in that at least one recess is of non-constant section along said central line.
 13. Blade set forth in claim 9, characterised in that it is made in titanium or one of its alloys. 